DESCRIPTION (Investigator's Abstract): Herpes simplex virus type 1 (HSV-1) is the most frequent agent of viral induced blindness, usually from corneal scarring following HSV-1 ocular recurrences (due to HSV-1 reactivations). Since LAT is the only HSV-1 gene active during neuronal latency, it is generally presumed that LAT plays an important role in latency and/or reactivation. Elucidation of the underlying molecular mechanisms behind the HSV-1 latency-reactivation cycle should lead to development of a means for reducing the incidence of HSV-1 induced blindness. The investigators plan to investigate the following three working hypotheses: 1. "LAT is involved in spontaneous reactivation in vivo." LAT mutants decrease ganglionic explant reactivation, but the parental strains of these mutants do not reactivate spontaneously. Thus, LAT's role in spontaneous reactivation remains to be confirmed and quantitated with mutants in a strain that does reactive spontaneously. 2. "Viral genes in addition to LAT are involved in HSV-1 latency and reactivation". LAT mutants decrease but do not abolish, explant reactivation. Therefore, additional viral genes must be involved. 3. "LAT makes a regulatory protein that can transactivate (up regulate) the ICP4 gene, thereby enhancing reactivation". LAT can transactivate ICP4. Restarting ICP4 synthesis is a logical first step in reactivation. An unreported open reading frame could encode a LAT protein that has that characteristics of DNA binding proteins. The investigators have detailed specific aims to test the above hypotheses and to further elucidate the molecular mechanisms by which HSV-1 establishes, maintains, and reactivates from latency include: 1. Analysis of a family of LAT mutants int he McKrae strain of HSV-1. McKrae has a high spontaneous reactivation rate, allowing us to test for involvement of LAT in spontaneous reactivation and to map the specific regions within LAT involved in spontaneous reactivation. (Addresses Hypothesis 1.) 2. Employ the differences in spontaneous reactivation between KOS (no spontaneous reactivation) and McKrae (high spontaneous reactivation) to determine if the LAT gene plays a role in reactivation. The investigators will replace the KOS LAT gene with the McKrae LAT gene and determine if the McKrae LAT gene can transfer the ability to spontaneously reactivate to KOS. (Addresses hypothesis 1.) 3. Characterize a proposed LAT protein that is potentially capable of transactivating ICP4 and hence enhancing spontaneous reactivation. Antibody against the expressed ORF will be used to look for a LAT protein during latency and reactivation. The regions of LAT and ICP4 involved in LAT's transactivation of ICP4 will be fine mapped. (Addresses hypothesis 2.) 4. Employ the differences in spontaneous reactivation between KOS and McKrae to find and map genes other than LAT that are involved in spontaneous reactivation. Sets of overlapping restriction fragments from McKrae and KOS will be reconstituted into infectious virus containing defined regions (and thus defined genes) from each strain. Spontaneous reactivation will be analyzed. (Addresses hypothesis 3.)